COIN-OR::LEMON - Graph Library

source: lemon-0.x/demo/lp_maxflow_demo.cc @ 1583:2b329fd595ef

Last change on this file since 1583:2b329fd595ef was 1583:2b329fd595ef, checked in by athos, 14 years ago

Documented some more demo programs.

File size: 3.4 KB
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1/* -*- C++ -*-
2 * demo/lp_maxflow_demo.cc - Part of LEMON, a generic C++ optimization library
3 *
4 * Copyright (C) 2005 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
5 * (Egervary Research Group on Combinatorial Optimization, EGRES).
6 *
7 * Permission to use, modify and distribute this software is granted
8 * provided that this copyright notice appears in all copies. For
9 * precise terms see the accompanying LICENSE file.
10 *
11 * This software is provided "AS IS" with no warranty of any kind,
12 * express or implied, and with no claim as to its suitability for any
13 * purpose.
14 *
15 */
16
17///\ingroup demos
18///\file
19///\brief Max flow problem solved with an LP solver (demo).
20///
21/// This demo program shows how to solve a maximum (or maximal) flow
22/// problem using the LEMON LP solver interface. We would like to lay
23/// the emphasis on the simplicity of the way one can formulate LP
24/// constraints that arise in graph theory in our library LEMON .
25
26#ifdef HAVE_CONFIG_H
27#include <config.h>
28#endif
29
30#include<lemon/graph_reader.h>
31#include<lemon/list_graph.h>
32
33#include <fstream>
34#include <iostream>
35
36
37#ifdef HAVE_GLPK
38#include <lemon/lp_glpk.h>
39#elif HAVE_CPLEX
40#include <lemon/lp_cplex.h>
41#endif
42
43using namespace lemon;
44
45#ifdef HAVE_GLPK
46typedef LpGlpk LpDefault;
47const char default_solver_name[]="GLPK";
48#elif HAVE_CPLEX
49typedef LpCplex LpDefault;
50const char default_solver_name[]="CPLEX";
51#endif
52
53
54template<class G,class C>
55double maxFlow(const G &g,const C &cap,typename G::Node s,typename G::Node t)
56{
57  LpDefault lp;
58 
59  typedef G Graph;
60  typedef typename G::Node Node;
61  typedef typename G::NodeIt NodeIt;
62  typedef typename G::Edge Edge;
63  typedef typename G::EdgeIt EdgeIt;
64  typedef typename G::OutEdgeIt OutEdgeIt;
65  typedef typename G::InEdgeIt InEdgeIt;
66 
67  //Define a map on the edges for the variables of the LP problem
68  typename G::template EdgeMap<LpDefault::Col> x(g);
69  lp.addColSet(x);
70 
71  //Nonnegativity and capacity constraints
72  for(EdgeIt e(g);e!=INVALID;++e) {
73    lp.colUpperBound(x[e],cap[e]);
74    lp.colLowerBound(x[e],0);
75  }
76
77
78  //Flow conservation constraints for the nodes (except for 's' and 't')
79  for(NodeIt n(g);n!=INVALID;++n) if(n!=s&&n!=t) {
80    LpDefault::Expr ex;
81    for(InEdgeIt  e(g,n);e!=INVALID;++e) ex+=x[e];
82    for(OutEdgeIt e(g,n);e!=INVALID;++e) ex-=x[e];
83    lp.addRow(ex==0);
84  }
85 
86  //Objective function: the flow value entering 't'
87  LpDefault::Expr obj;
88  for(InEdgeIt  e(g,t);e!=INVALID;++e) obj+=x[e];
89  for(OutEdgeIt e(g,t);e!=INVALID;++e) obj-=x[e];
90  lp.setObj(obj);
91
92
93  //Maximization
94  lp.max();
95
96#ifdef HAVE_GLPK
97  lp.presolver(true);
98  lp.messageLevel(3);
99#endif
100
101  std::cout<<"Solver used: "<<default_solver_name<<std::endl;
102
103  //Solve with the underlying solver
104  lp.solve();
105
106  return lp.primalValue();
107}
108
109int main(int argc, char *argv[])
110{
111  if(argc<2)
112  {
113      std::cerr << "  USAGE: lp_maxflow_demo input_file.lgf" << std::endl;
114      std::cerr << "  The file 'input_file.lgf' has to contain a max "
115                << "flow instance in\n"
116                << "  LEMON format (e.g. sample.lgf is such a file)."
117                << std::endl;
118      return 0;
119  }
120
121
122  //input stream to read the graph from
123  std::ifstream is(argv[1]);
124
125
126  ListGraph g;
127  ListGraph::Node s;
128  ListGraph::Node t;
129 
130  ListGraph::EdgeMap<double> cap(g);
131 
132  GraphReader<ListGraph> reader(is,g);
133  reader.readNode("source",s).readNode("target",t)
134    .readEdgeMap("capacity",cap).run();
135 
136  std::cout << "Max flow value = " << maxFlow(g,cap,s,t) << std::endl;
137
138}
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